An electron beam microscope directs an electron beam onto a sample. The electrons of the beam interact with the sample and generate radiation, such as x-ray photons and backscattered electrons, detected by an energy-sensitive detector. The energy-sensitive detector generates detection signals, having a signal intensity corresponding to the energy of the detected radiation. The detection signals are processed by a signal processor typically including an analog amplifier, an analog-to-digital converter and subsequent electronics to analyze the signal heights of the digital signals. The subsequent electronics limit the count rate which can be detected.
Energy-sensitive detectors are used for performing energy-dispersive x-ray spectroscopy (EDX), in which x-ray photons generated by the electrons impinging on the sample are detected in dependence of the energy, wherein a suitable window, such as a thin membrane, prevents backscattered electrons from reaching the detector. If the window is not used, the detector is also able to detect backscattered electrons, and the backscattered electrons will predominantly contribute to the detection signals since the number of generated backscattered electrons is much higher than the number of generated x-ray photons. However, in such mode of operation, the electron beam current is limited to a few picoamperes since the subsequent electronics limit the maximum count rate which can be processed.
US 2013/0099114 A1 discloses an electron beam microscope having a silicon drift diode (SDD) as its energy-sensitive detector. The detector can be operated in two different modes: a “pulse height measuring mode” in which the signal intensity can be analyzed and which is used for the detection of x-ray photons when a window blocks backscattered electrons from being incident on the detector, and a “current measuring mode” used for the detection of backscattered electrons at higher beam currents and in which the output signal of the detector depends on the number of electron/hole pairs per time unit generated in the detector. While the “current measuring mode” of this electron beam microscope allows detection of backscattered electrons at higher beam currents using a silicon drift diode, the detector does not allow for an energy analysis of the detected backscattered electrons.